I'll start by prefacing my question by saying I've read the threads about supplements and this is a question more about what you would do if your professor said this to you.

So I went out and purchased a Farnsworth on Ks hornbook off Amazon earlier today. I bought it not because my professor recommended it, but because of its reputation. My professor had not mentioned supplements at all and I probably should have asked before hand but I thought that the hornbook was a different animal than say an E&E or a Gilbert. Literally 2 hours after I ordered the hornbook (today), during Ks, she decided to just tell the class about what supplements she thought were the best. She recommended C&P on Ks, but she prefaced it by the fact that the sole reason for her preference was the hornbook's readability. She said the Farnsworth hornbook was too dense for her when she took Ks.

Should I go cancel my order for Farnsworth and pick up the C&P (which is $25 more expensive but a more recent edition) or do you think I should be fine with Farnsworth?

I have C&P and it is good.That said, if it's too late to cancel your Farnsworth I wouldn't sweat it. It will certainly be a big help. But if you CAN switch it for the one your prof recommends, do that.